1. Technical Field
This invention relates to an image forming apparatus having a determining device that determines a deterioration degree of a latent image bearer based on a result of detecting a surface potential of the latent image bearer.
2. Related Art
Conventionally, an image forming apparatus to form an image by using the below described electro-photography is known. Specifically, a surface of a latent image bearer is uniformly charged electrically by an electric charger such as a corona charger, etc. Subsequently, a latent image having a potential different from (e.g., opposite) the uniformly charge potential is written onto the latent image bearer by executing optical scanning. Subsequently, the latent image on the latent image bearer is developed by a developing unit as it selectively attaches toner thereto. While transferring the toner image obtained in this way onto a recording sheet by either directly or indirectly via an intermediate transferring member, the recording sheet with the toner image is output. Subsequently, residual electric charge is removed from the latent image bearer by an electric charge-removing device after the toner image is transferred therefrom. Subsequently, to prepare for the next latent image formation, the latent image bearer is uniformly charged again by the electric charger.
In such a system that conducts the electro-photography, as the latent image bearer repeats charging uniformly, writing the latent image, and removing the electric charge remaining on the latent image bearer, charging performance gradually deteriorates. Consequently, the latent image bearer markedly degrades the charging performance and becomes difficult to form a latent image with a stable potential thereby degrading image quality.
In a conventional image forming apparatus, immediately after a surface of a rotatable drum-type photoconductor as a latent image bearer is uniformly charged by an electric charger, a voltage sensor detects the uniformly charged potential. When the detection result is below a prescribed lower limit, the photoconductor is regarded as deteriorated and reaches the end of its working life, and is replaced with a new photoconductor.
By encouraging the user to replace the old photoconductor with the new photoconductor before the old photoconductor degrades to the point where it is difficult to form a latent image with a stable potential, image deterioration caused by such deterioration of the photoconductor can be minimized.
However, when a deterioration degree of the photoconductor is not uniform axially, the expiration of the photoconductor cannot be timely detected and may cause the deterioration of image quality.
Further, as a frequency of writing latent images on the photoconductor increases, the photoconductor is more quickly degraded. Accordingly, when the frequency of writing the latent image on the photoconductor deviates axially, the deterioration degree of photoconductor also deviates according to the deviation of the writing frequency. That is, in a region in which the latent images are relatively frequently written, deterioration progresses rapidly. By contrast, in another region in which the latent images are relatively rarely written, the deterioration does not progress rapidly.
Although the deterioration degree of the photoconductor deviates axially in this way, only a potential of a central region out of the whole region of the photoconductor axially is detected by a voltage sensor and whether or not the photoconductor as a whole has worn out is determined based only on its detection result in the conventional image forming apparatus. With such a system, however, when a side region more quickly deteriorates and wears out than a central region, such an effect cannot be detected and may end up causing deterioration of image quality.